Heretofore, particularly in medical wards, a determination of a plurality of sleep stages has been made based on a polysomnographic technique designed to acquire data about electroencephalogram electrooculogram and sub-mental electromyogram, and discriminate the sleep stages based on the acquired data. Unfortunately, this technique is unsuitable for general households, because the measurement for acquiring the data involves a troublesome preparatory step of attaching a plurality of electrodes onto the body of a human subject, and requires expertise in handling measuring devices.
Form this standpoint, an apparatus has been disclosed that is designed to detect at least one of a gross body movement and a heart rate of a human subject on bedclothes using a vibration sensor, such as a piezoelectric element, disposed under bedclothes designed, and calculate an occurrence number of gross body movements or a heart-rate variation based on the detected data, so as to discriminate a plurality of sleep stages based on a correlation between the calculated data and a sleep cycle (see, for example, the following Patent Publication 1).                [Parent Publication 1] Japanese Patent Laid-Open Publication No. 2002-219116        